The present invention is directed to a golf ball having a controlled variable moment of inertia. Particularly, the golf ball includes at least one hollow channel. At least one movable weight is located in the hollow channel near the center of the golf ball at rest, and moves outwardly as the spin rate of the ball increases. The movable weight returns towards the center of the golf ball as the spin rate decreases. The change in the radial position of the movable weight alters the moment of rotational inertia of the ball. The position of the weight within the channel is controlled, such as by a spring or spring-like device, magnetic force, etc. The present invention is also directed to a method for making a golf ball having a controlled variable moment of inertia.
Moment of inertia is the sum of the products formed by multiplying the mass of each part of an assembly by the square of its distance from a specified axis plus the moment of inertia of each part about its own center of mass. It is also sometimes referenced as rotational inertia. In spherical objects, such as a golf ball, a low moment of inertia means that a larger portion of its mass is concentrated in the center. In turn, a high moment of inertia means that more of its mass is concentrated towards the outer cover or periphery of the sphere or ball.
Moment of inertia (xe2x80x9cMOIxe2x80x9d) affects the playability of a golf ball in many ways. For example, moment of inertia affects the amount of spin produced when the golf ball is struck with a wood or iron. This may result in a desirable characteristic (i.e. high spin for ball placement, low spin for enhanced distance, etc.) or an undesirable characteristic (i.e. hooking or slicing, etc.) depending upon the skill level of the golfer, the type of club used, etc. Moment of inertia also affects the overall trajectory of a ball and thus, often the overall distance the ball will travel. Also, moment of inertia affects the short game, including lofting, pitching, chipping, and putting.
For some aspects of the golf game, it is desirable to have a golf ball that exhibits a relatively high moment of rotational inertia, for example in which the mass of the ball located near the outer periphery of the ball is greater than the mass of the ball located near the center of the ball. A golf ball exhibiting a high moment of inertia generally has a reduced rate of spin, including reduced side spin, so that such a ball may be desired for certain shots requiring distance. A low spin ball also produces less side spin, thus reducing the amount of hooking and slicing.
Although a golf ball exhibiting a relatively high moment of inertia has certain desirable properties at different club head speeds and with different lofted clubs, it may also possess undesirable characteristics. Furthermore, such a ball may lack the necessary feel and roll characteristics for the short game, particularly putting.
Therefore, for certain aspects of the golf game, it would be desirable for a golf ball to exhibit a relatively low moment of inertia, where the mass of the ball near the center of the ball is greater than the mass of the ball near the outer portion of the ball. As noted, in some applications, a golf ball exhibiting a relatively low moment of inertia is desirable, such as for the short game where high spin allows a skilled golfer to more easily position his/her ball on the green, etc. In turn, it is also desirable in certain situations for a golf ball to exhibit a relatively high moment of inertia, such as for the long game where enhanced distance is desirable.
Currently, golf balls having a relatively low or high fixed moment of inertia are commercially available or are known in the art. For example, U.S. Pat. No. 5,026,067 teaches a golf ball having a cover or intermediate layer with a specific gravity greater than the center, giving the golf ball a relatively high moment of inertia. Also, U.S. Pat. No. 6,010,912 teaches a golf ball having a low specific gravity core and a high specific gravity layer surrounding the core so that the golf ball has a relatively high moment of inertia. Conversely, U.S. Pat. No. 6,180,722 teaches a golf ball having a specific gravity near the center of the ball greater than the layer surrounding the center so that such a ball has a relatively low moment of inertia.
Players, depending upon their skill and preferences relating to the features of a golf ball, may choose a golf ball having a relatively high moment of inertia in order to increase distance and/or reduce the amount of slicing or hooking when driving, or a golf ball having a relatively low moment of inertia for improved feel, placement, etc., near or on the green. Unfortunately, a golfer choosing either a high or low moment of inertia golf ball in order to promote certain aspects of the game risks suffering deficiencies in other aspects of the game.
In the past, golf and/or game balls have been formed where the movement of inertia of the ball randomly varies. U.S. Pat. No. 1,120,757 discloses a game ball having a spherical ball that randomly moves within the chambers of the game ball when the game ball rotates. The springs described in that patent are used to ensure that the spherical ball does not maintain a position near the outer periphery of the game ball. That is, the springs cause the spherical ball to rebound from the outer periphery of the game ball toward the center of the game ball, thereby preventing the spherical ball from remaining in one chamber while the game ball is in action. The design of the game ball in the ""757 patent causes the center of gravity, also known as the center of mass, of the game ball to randomly vary as the game ball rotates as a result of the random movement of the spherical ball within the interior of the game ball. This design causes peculiar gyration and movement of the game ball along paths that are impossible to determine with any degree of accuracy.
U.S. Pat. Nos. 728,311; 737,032; and 2,859,968 are directed to various balls that have a hollow portion in the center of the ball and one or more smaller balls within the hollow portion. When the ball rotates, the smaller ball or balls in the hollow portion freely moves in an uncontrolled fashion within the ball. None of the balls disclosed in these patents has a controlled variable moment of inertia which would maximize the playability and feel desired in a golf ball.
Accordingly, it would be useful to develop a golf ball having a controlled variable moment of inertia such that the golf ball exhibits low moment of inertia properties that are desirable during short distance play and also exhibits high moment of inertia properties that are desirable during longer distance play. In particular, it would be desirable to provide a golf ball having a moment of rotational inertia that may be selectively varied.
Accordingly, it is a feature of the present invention to provide a golf ball having a controlled variable moment of inertia. In a first aspect of the present invention, a golf ball is provided which has at least one hollow channel. At least one end of the hollow channel is located along the outer periphery of the ball. At least one movable weight is located in the hollow channel. A positioning member such as a spring, which is in constant contact with the movable weight, controls the movement and position of the weight within the hollow channel. A plug encloses the end of the hollow channel along the outer edge of the ball.
In a second aspect, the present invention provides a golf ball comprising a core defining at least one hollow channel. The hollow channel has at least one end at the outer edge of the core. At least one movable weight comprising a magnet is located in the hollow channel. A plug also comprising a magnet encloses the end of the hollow channel at the outer edge of the core. The magnetic polarity of the end or face of the movable weight nearest the plug is the same as the portion of the plug nearest the weight.
In another aspect, the present invention provides a golf ball having a core defining at least one hollow channel. The hollow channel has at least one end at the outer edge of the core. At least one movable weight and a spring in continuous contact with the weight are located in the hollow channel. A plug encloses the end of the hollow channel at the outer edge of the core. The movable weight is positioned between the spring and plug.
In an additional aspect, the present invention provides a golf ball having a moment of rotational inertia that changes depending upon the spin rate of the ball. The golf ball preferably comprises a generally spherical core which defines one or more radially extending channels within the interior of the core. The ball further preferably comprises one or more spherical components, each positioned and movable within a respective channel. The ball also comprises one or more springs, each also positioned in a respective channel and in continuous contact with a corresponding spherical component. Upon sufficient rotation of the ball, each of the spherical components is displaced radially outward within a corresponding channel, thereby altering the moment of rotational inertia of the ball.
In a further aspect, the present invention provides one or more methods for promoting particular types of spin to a golf ball. In these techniques, a golf ball according to the present invention is positioned on a hitting surface such as a golf tee so that particular interior components of the ball are oriented in either a generally horizontal or vertical plane.
In yet another aspect, the present invention provides a method for making a golf ball having a controlled variable moment of inertia. The method includes preparing a ball; drilling into the ball from the outer edge to form at least one hollow channel; inserting at least one movable weight into the hollow channel; inserting a spring into the hollow channel that is in continuous contact with the weight; and enclosing the end of the hollow channel at the outer edge of the ball with a plug.
These and other objects and features of the invention will be apparent from the detailed description set forth below.